Numerical Simulation On Atmospheric Pressure Low-temperature Plasma Jet

Atmospheric pressure non-equilibrium plasma jets (APNP-Js) are receiving increasing attention for its promise applications, such as plasma medicine, biomedical engineering, materials processing, and synthesis, which is also hot topic for plasma science and technology in this field. Recently, numerous experiments and numerical modeling researches on APNP-Js have been presented. However, due to the complicate behavior of plasma jets, especially strong non-linear effects of spatial expansion dissipative discharge system, the mechanism of APNP-Js remains unknown. In this work, a two-dimensional hydrodynamic model, solving the Poisson equation coupled with drift-diffusion equation, is used to investigate the mechanism of APNP-Js. More specifically, the modeling results are presented in the following:The characteristics of pure helium plasma jets including the dynamics of electric field, electron density, ionization rate in plasma jets and the effects of power parameters, working gas, and photoionization and background ionization, are studied. The modeling results show that (1) the velocity of plasma bullet increases with the increase of applied voltage;(2) The length of the plasma increases with shorter pulse rise time and decrease of the radius of plasma jets;(3) When the seed electrons produced by photoionization ahead of plasma bullet is much lower than that provided by background ionization, the propagation of plasma bullets is repeatable.The effects of different parameters, including the air diffusion, polarity of the external voltage, Penning ionization, and seed electrons density on the dynamics of the plasma jets in the open air, are investigated. The modeling results depict that (1) due to the air diffusion, the plasma bullet propagates slower, the length of plasma jets is shorter than that in pure helium plasma jets;(2) The characteristics of plasma jets are different between positive and negative pulse voltages. The length of plasma jet for positive pulse voltage is longer than that for negative pulse voltage. The plasma bullet head has a spherical form and sword-like form for positive and negative pulse voltages, respectively.(3) The Penning ionization is not essential to the donut-shape structure of plasma bullet, but plays an important role in the propagation of plasma plume.(4) Seed electron density is expected to play a significant role in the formation and propagation of plasma jets. It’s found that the structure of streamer head is not bullet-like form any more when the seed electron density is pretty high.The effects of floating electrode on the plasma jets. In the experiment, a continuum dark column inside the floating electrode is observed by naked eye. Dynamics of the discharge shows that primary plasma bullet propagates relatively slow and extinguishes at one end of the floating electrode. After tens of nanoseconds, a secondary plasma bullet is ignited at another end of the floating electrode. Modeling results indicates that, when the plasma bullet approaches to the floating electrode, the potential on the floating electrode increases, the electric field inside the floating electrode decreases to a lower value which can’t sustain the discharge, but the electric field near the end of the floating electrode becomes stronger, which explains the formation of the dark column and the ignition of the secondary plasma bullet. These modeling results are consistent with the experimental results...